The objective of this study of blood rheology is a collaborative interdisciplinary effort to characterize the biochemical and physical properties of blood cells and their membranes, and of fibrin, as these properties have significance to release of maturing erythrocytes and leukocytes from marrow; contribute to flow behavior in the microcirculation; and as they pertain to microvascular occlusive phenomena, including fibrin clot formation and thrombolysis. The efforts focus on the physiological processes of marrow egress, flow in microvasculature and in occlusion, and combine the experimental approaches to issues of clinical importance with the analytical and theoretical contributions of engineering scientists and biophysicists. The Core provides administrative, management and advisory functions. Project 1 examines marrow release phenomena; 2 is concerned with fibrin and products in clot production and lysis, and with in vitro studies in flow channels and vessel replicas; 3, studies of erythrocyte membrane protein structure and function; 4, development of methods for measurement of single cell nucleotides and correlation with shape; 5, correlation of erythrocyte and leukocyte membrane properties with capillary flow behavior; 6, investigation of erythrocyte deformability in in vitro flow systems; 7, theoretical mathematical models of transport and particle behavior in capillaries; 8, development of optical imaging methods to enhance cell shape studies; and 9, theoretical and experimental studies of erythrocyte shape and aggregation.